Probing the surface active sites of Ce1−xNixO2-δ for catalytic reduction of NO

Abstract

Understanding the underlying mechanism of NO reduction on supported metal catalysts has been a long standing challenge. Herein, we report an integrated experimental cum theoretical probe to elucidate the surface active sites vis à vis the plausible reaction mechanism to comprehend the catalytic reduction of NO over solid solutions of Ce1−xNixO2-δ. In the as-prepared solid solutions of phase pure Ce1−xNixO2-δ, minor component of Ni2+ substituted Ce4+ at the Wyckoff sites 4a resulting in a uniform distribution Ni2+ within the crystal lattice of the parent fluorite CeO2. The as-prepared material exhibited a higher catalytic efficacy towards NO reduction in comparison with the Ni or NiO dispersed over CeO2 support. The catalytic efficacy was further enhanced with reduced Ce1−xNixO2-δ due to the presence of excess oxygen vacancies and surface hydroxyl species. The important role of oxygen vacancies and surface hydroxyl species as active sites in the reaction mechanism was further corroborated by DFT calculations. A generalized kinetic model was developed that could identify the rate determining step for the NO reduction mechanism by H2 over supported metal catalysts Ce1−xNixO2-δ.